The present invention relates to a cooling arrangement and, more particularly, to a cooling arrangement utilised in a gas turbine engine with regard to inter-blade platforms.
It will be understood that the efficiency and output of a gas turbine engine is related directly to turbine gas temperature. In such circumstances it is desirable to operate a gas turbine engine at the highest temperature possible. At such temperatures it is necessary to provide cooling of components within the gas turbine engine in order to remain within acceptable temperature ranges for the materials from which various components are formed.
One of the most difficult locations to cool in a gas turbine engine is the inter-blade platform structure of the high-pressure turbine stage. In the past, embedded convective holes have been used, along with various film cooling configurations. However, these cooling schemes have proved problematic from a stress concentration point of view. The platform gas washed surfaces are highly-stressed both mechanically, due to the centrifugal loading, and thermally, due to the temperature gradients present. Drilling cooling holes has been successful in reducing the metal temperature level associated thermal gradients but these holes have significantly increased the local three-dimensional stress levels in the component and so have been counter-productive in terms of a desire for improved extension of component life.
More recently, as described in U.K. Patent application number 0304329.6, a cooling arrangement has been proposed which utilises a damper below a junction between platforms in order to release coolant. It will be understood that cooling air taken from the compressor used to cool the hot turbines is not used to extract work from the turbine. Extracting coolant, therefore, has an adverse effect on engine operating efficiency and it is, therefore, necessary to utilise cooling air as effectively as possible in order to reduce the amount of cooling air extracted. The controlled leakage of coolant through a series of staggered slots machined or cast into contact surfaces of a “Cottage Roof” damper is used to provide cooling about the platform. The coolant air is used initially to cool the disc post or zone between two disc fir tree mounting root serrations and this is bled from the cavity beneath the blade platform surfaces through the slots in the damper surface in order to cool the surfaces of the damper and the platform edges and then the coolant emerges into the gap or junction between two neighbouring platforms. The spent coolant then impingement cools the adjacent platform edge before escaping radially into the gas path and becoming entrained with the strong hot gas flows about the platform.
Although the “Slotted Cottage Roof Damper” arrangement described in the UK Patent application 0304329.6 provides distinct improvements and advantages over the previous approach, it will be appreciated that improvements can still be made. A primary disadvantage relates to the angle and, to a lesser extent, the velocity of the spent coolant emerging from the junction gap between neighbouring platform edges. In short, the spent coolant rapidly mixes with the hot gas-flows and, therefore, does not provide any significant cooling effect.